In recent years, there are growing trends of high-speed processing and save of a large data with the rise of the digital technology. Consequently, a higher integration density and a higher performance are demanded in the semiconductor device equipped in the electronic equipment.
As to a semiconductor memory device, for example, in order to realize a higher integration density of DRAM (Dynamic Random Access Memory), the technology to employ a ferroelectric material or a high-dielectric material as a capacitor insulating film of a capacitor element constituting DRAM, instead of the conventional silicon oxide or silicon nitride, is widely researched and developed.
As the nonvolatile memory that does not lose the stored information even after a power supply is cut off, the flash memory and the ferroelectric memory (FeRAM: Ferroelectric Random Access Memory) are known until now.
The flash memory has a floating gate that is embedded in a gate insulating film of an insulated-gate field effect transistor (IGFET), and stores the information by accumulating the charges representing the stored information in the floating gate. A tunnel current passing through the insulating film must be fed to write/erase the information, and a relatively high voltage is needed.
Also, in order to realize the nonvolatile RAM that can execute a writing operation and a reading operation quickly at a lower voltage, the technology to employ a ferroelectric film having the spontaneous polarization characteristic as a capacitor insulating film is eagerly researched and developed. The semiconductor memory device having such ferroelectric capacitor insulating film is called a ferroelectric memory (FeRAM)
The FeRAM stores the information by utilizing the hysteresis characteristic of the ferroelectric substance. The ferroelectric capacitor structure in which the ferroelectric film is put between a pair of electrodes is provided to the ferroelectric memory produces a polarization in response to an applied voltage between the electrodes, and keeps a spontaneous polarization even after the applied voltage is removed. Also, the polarity of the spontaneous polarization is inverted when the polarity of the applied voltage is inverted. Therefore, the information can be read by sensing this spontaneous polarization.
The ferroelectric memory operates at a low voltage rather than a flash memory, and can execute a speedup writing while achieving a power saving. A study of the logic combined chip (SOC: System On Chip), in which the FeRAM is combined with the conventional logic technology, as the applications of the IC card, etc. is now conducted.
The ferroelectric film constituting the capacitor of FeRAM is formed of lead zirconate titanate (PZT), PZT in which La is doped (PLZT), PLZT-based material in which Ca, Sr, or Si is micro-doped, a hi-layer structure compound such as SrBi2Ta2O9(SBT, YI), SrBi2(Ta, Nb)2O9(SBTN, YZ), or the like. Such ferroelectric film is formed by the sol-gel method, the sputter method, the MOCVD (Metal Organic Chemical Vapor Deposition) method, or the like.
Normally, an amorphous or microcrystalline ferroelectric film is formed on the lower electrode by the above film forming method, and then the crystal structure is changed into the perovskite structure or the bismuth layer structure by the subsequent heat treatment. Also, a film quality is improved by oxidation after the ferroelectric film is formed.
Therefore, as the electrode material of the capacitor, the material that is hard to oxidize or the material that can maintain conductivity even after oxidized must be employed. Commonly, either a platinum based metal such as Pt (platinum), Ir (iridium), IrOx (iridium oxide), or the like or its oxide is widely employed. Also, it is common that, as the wiring material, Al (aluminum) is employed like the normal semiconductor device.
In the FeRAM, such a problem existed that the ferroelectric film is ready to deteriorate by the hydrogen that is produced in various steps after the ferroelectric capacitor structure is formed, and the like. Therefore, in order to protect the ferroelectric film from the hydrogen, etc., the technology to form the upper electrode by using the conductive oxide such as iridium oxide (IrOz), or the like, for example has been presented.
However, it may be considered that, when the conductive oxide is employed as the material of the upper electrode, the oxygen contributes to the block of the hydrogen, etc., nevertheless such a problem arises that the underlying film of the connection plug, e.g., Ti, TiN, or the like, positioned right on the upper electrode is oxidized by the emitted oxygen to bring about an increase of a contact resistance. Therefore, the technology to prevent oxidation of the underlying film by forming the oxidation-resistant metal film such as iridium (Ir), or the like on the conductive oxide has been presented.
Further, following structures are disclosed as the capacitor electrode.
In Japanese Laid-open Patent Application Publication No. JP 2002-3244894-A, it is set forth that, when the upper electrode formed on ferroelectric film is constructed by the first conductive oxide film and the second conductive oxide film such that the second conductive oxide film is formed to have a composition that is closer to a stoichiometric composition than the first conductive oxide film, the electric characteristics of the ferroelectric capacitor can be finely patterned without deterioration during the step of constructing the multilayer wiring.
In Japanese Laid-open Patent Application Publication No. JP 2003-17581-A, the semiconductor device equipped with the capacitor having such a structure that at least one of the upper electrode and the lower electrode is formed of a titanium aluminum nitride layer represented by TixAl1-xN (x=0.05 to 0.5) and the high-dielectric metal oxide film such as tantalum oxide, or the like is put between the upper electrode and the lower electrode constructed as above is set forth.
In Japanese Laid-open Patent Application Publication No. JP 2003-100912-A, it is set forth that, when the capacitor upper electrode is formed of Pt and then an oxidation-resistant TiAlN barrier film is provided onto the upper electrode, the deterioration of the characteristics of the capacitor insulating film caused due to the exposure of the upper electrode is avoided.
In Japanese Laid-open Patent Application Publication No. JP 2006-32451-A, it is proposed that, in order to prevent the deterioration of the contact plug cause by a catalytic action of hydrogen, the capacitor lower electrode on the contact plug is formed on a Pt/IrOx/Ir/TiAlN stacked layer structure.
In Japanese Laid-open Patent Application Publication No. JP 2003-258201-A, a method of etching collectively the constitutive films of the capacitor by using the hard mask is disclosed. In this case, the material of the oxygen barrier film is formed of TiN, TiAlN, Ir, or their oxide, or Ru, RuOx.
In Japanese Laid-open Patent Application Publication No. JP2003-152165-A, it is proposed that, when such a method is employed that the contact holes that expose the upper electrode of the ferroelectric capacitor are formed in the insulating film, then an adhesive film made of TiN is formed in the contact holes after the annealing in an oxidizing atmosphere, and then the W film is stacked/filled in the contact holes by the CVD method while using such TiN adhesive film as a hydrogen barrier, deterioration of the characteristic of the ferroelectric capacitor is prevented.